In the spirit of TIMTOWTDI, I offer my version from my FPBASIC days:

my $num=42;
my $padto="000000"; # padding to 6digs

$num=$padto.$num;

print substr($num,-6), "\n";
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Not the shortest, but a valid solution. Of course, I'd use printf() as mentioned zillions of times.

--
Me spell chucker work grate. Need grandma chicken.